Data on historical evolution of different crop cultivars in seventy years
were further analyzed and big and small cycle of improvement of yield ability,
alternating cycle improvement among number of ear per unit area, seed weight
per ear, light absorption coefficient in community (or plant type), was first
found. Each of big cycle was forty years. First big cycle from 1940 to late
1970, cross breeding was conducted on basis of arrangement and evaluation
of local variety under situation of maintaining original and no improved plant
type characteristics. The second big cycle since late seventies in twenty
century on the basis of first improvement of plant type was started and underwent
forty years. At present this big cycle was about ended. Third big cycle on
basis of second plant type improvement should be forty years from 2020 to
2059. There were four small cycles in a big cycle, each of small cycle
should be about decade. In each of four small cycles number of ear (or number
of plant) and seed weight per ear should be alternatively or together
heightened. In improvement of most ear type variety change of plant type were
very obvious, but in biggest ear type breeding not obvious and in middle type
breeding gradually obvious. On basis of cycle phenomenon and tree types of
yield ability improvement author point out that breeding target of tree yield
ability types, most ear type, biggest ear type and middle type, should be persisted,
three parent combination ways, most ear × most ear, biggest ear × biggest ear
and most ear × biggest ear should be persisted. Especially, selection for two
extreme types should be first accomplished enhancing and development of middle
type could be guided.